Scientists use high-voltage tiny solar panels to convert laser light into electricity

A team of scientists led by the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) has designed a single-crystal miniature solar panel that can convert laser light into electricity.

"The technology is inexpensive because it is silicon-based and uses the same process as ground-based cells, such as TOPCon devices that rely on silicon oxide passivation contacts," Paul Stradins, lead author of the study, told the Journal Photovoltaics. "The module consists of a polycrystalline silicon/silica passivated contact micro cell. These tiny cells have very low contact resistance and are suitable for operation in high sunlight."

In the paper "High-power Laser Power Conversion of high-voltage monocrystal silicon photovoltaic micromodules based on polycrystalline silicon /SiO x passivated contacts," published in Solar Materials and Solar Cells, the scientists explain that the panel could be used for applications such as wireless data transmission in special environments or energy transmission in medical implants, for example.

The multi-junction mini-panel features a silicon oxide (polysilicon /SiOx) passivated contact design using a very thin SiOx layer of about 1.5 nm. These passivation contacts are used to build miniature batteries that reportedly have very low contact resistance and are suitable for operation in high sunlight. The miniature battery is placed on the "edge" and loaded into the module.

"These tiny cells can be formed into tiny modules by simple mechanical stacking," says Stradins. "We used 10 batteries, but it could be any number. So the voltage of these micro-modules can be very high while the current stays low."

In solar modules, the direct contact of metals from one cell to the next allows current to flow freely between them, and the large area of contact limits the series resistance. The light passes vertically through the narrow edge of the device, and the current is collected laterally through the large area of P-type and N-type passivation contacts.

According to the researchers, this architecture allows the collection of battery current across the entire "side" region of the tiny cell, which is much larger than the area where light enters. "These stacks of 10 or more tiny cells can be assembled into higher power emission conversion modules of any size," Stradins further explains. "There is no size limit, it can be meters if needed, and there are cooling, connection and power electronics on the back."

The team tested the module at around 1000 nm of illumination and found that its photoelectric conversion efficiency was over 40%, its open-circuit voltage was over 7 V, and its fill factor was about 78%. "Based on current equipment results, it is expected that a 10 cm2 module can obtain 25 W of power transmission using a 12 kW laser source over a distance of 1 km," the academics said.

According to Stradins, the tiny cells can be made without any expensive lithography techniques. "We use mechanically aligned masks for all deposition steps, which can be easily done with ns laser scribers," he said. "Micro batteries are also produced by the same laser marking process. They remain attached to the wafer and are processed as a whole, suitable for all steps including final metallization. They are then disassembled and assembled into tiny modules. All of this can be automated on the production line."

Source: Laser Network